The effects of earthquakes will be well known. Even when seismic activity is relatively minor, combinations of horizontal, vertical and rotational forces induce not insignificant stresses within structures connected to the ground. Such structures may include buildings, nonbuilding structures, building foundations and infrastructure (for example, road networks and power transmission networks).
If the seismic activity is more significant, so too are the induced stresses. This leads to an increased risk of damage to structures. Such damage can be costly to repair and may render a particular structure temporarily unusable. If the damage is sufficiently extensive, there is the risk of total structural failure which, in worst case scenarios, can result in the complete loss of the structure and even injury or the loss of lives.
In addition to the risks presented to the structures themselves, there are also risks to objects within or on such structures. Such objects may be damaged and present further risks of damage and injury.
As the mechanisms behind earthquakes have become better understood, there has been an improvement in the engineering of structures so as to be able to withstand earthquakes and make them safer. Those skilled in the art will appreciate that there are many aspects of earthquake engineering that improves a structure's performance under seismic activity. This includes improved and stronger building materials, improved designs, installation of tuned mass dampeners and installation of bearings.
Bearings, also known as base isolators, help minimise the effect of seismic activity by providing a connection that decouples a substructure (e.g. the ground) from the superstructure thereby reducing the forces applied to the structure. In turn this lessens the potential for damage to the structure and to objects within or on the structure. There are essentially two aspects to bearing design: isolation and dampening.
Isolation aims to minimise the transfer of forces from the substructure to the superstructure by creating a functional separation between the two structures. For example, WO2004/079113 discloses a sliding bearing with a vertical support that slides relative to an adjacent surface. The sliding bearing includes a diaphragm which acts to restore the vertical support to a central position. Though this sliding bearing can lessen the effects of horizontal and rotational forces, it would not perform well under vertical forces. Further, the design is complex and is therefore expensive.
Dampening aims to absorb the energy of forces applied to the substructure to lessen the severity of forces transferred to the superstructure. For example, lead-rubber bearings comprise a rubber column with lead inserts (such as lead plates or rods). Under seismic forces the rubber dampens forces, with the lead acting to absorb a significant amount of energy. Under light loading, the bearing will return to its normal position following the removal of the load. However, under significant loading, the lead inserts may irreversibly deform, requiring the bearing to be replaced. Lead rubber bearings are also complex to manufacture and are therefore expensive. They are also difficult and expensive to replace.
It is an object of the invention to provide a resilient bearing that alleviates at least some of the problems identified above.
It is also an object of the invention to provide a resilient bearing that is inexpensive to manufacture, performs well under all directional forces and is easy to install.
Each object is to be read disjunctively with the object of at least providing the public with a useful choice.
It is acknowledged that the terms “comprise”, “comprises” and “comprising” may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, these terms are intended to have an inclusive meaning—i.e. they will be taken to mean an inclusion of the listed components which the use directly references, and possibly also of other non-specified components or elements.
Reference to any prior art in this specification does not constitute an admission that such prior art forms part of the common general knowledge.